feat: improve user controller

Author: junjie-w

src/main/java/com/example/jwt_auth_server/controller/UserController.java

@@ -1,16 +1,19 @@
 package com.example.jwt_auth_server.controller;
 
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import org.springframework.http.ResponseEntity;
+import org.springframework.security.access.prepost.PreAuthorize;
 import org.springframework.security.core.Authentication;
 import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.security.core.userdetails.UsernameNotFoundException;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 
+import com.example.jwt_auth_server.model.User;
 import com.example.jwt_auth_server.service.UserService;
 
 @RestController
@@ -23,6 +26,13 @@ public UserController(UserService userService) {
         this.userService = userService;
     }
 
+    @GetMapping
+    @PreAuthorize("hasRole('ADMIN')")
+    public ResponseEntity<List<User>> getAllUsers() {
+        List<User> users = userService.getAllUsers();
+        return ResponseEntity.ok(users);
+    }
+
     @GetMapping("/me")
     public ResponseEntity<?> getCurrentUser() {
         Authentication authentication = SecurityContextHolder.getContext().getAuthentication();